I've been skeptical of Amazon ever since I learned that they bin inventory from all sellers together at the warehouse, so you could pay extra to buy from the manufacturer's official store and still be sent a cheap knockoff.
(The fact that this information is so important and hidden is of course inexcusable)
If the ASIN was different it wouldn't be comingled, but I don't think Amazon wants sellers all creating their own ASINs and thus new product pages when one already exists for the product.
Anybody who has used Amazon enough has witnessed when there's multiple separate listings for the same product and how annoying it is to compare.